Difference Betwixt @Component, @Service, @Controller, Together With @Repository Inward Spring

Before you lot larn the departure betwixt @Component, @Service, @Controller, in addition to @Repository annotations inward Spring framework, it's of import to empathize the role of @Component annotation inward Spring. During initial liberate of Spring, all beans are used to live on declared inward an XML file. For a large project, this chop-chop becomes a massive chore in addition to Spring guys recognize the work rather quickly. In after versions, they render annotation-based dependency injection in addition to Java-based configuration. From Spring 2.5 annotation-based dependency injection was introduced, which automatically scans in addition to register classes equally Spring edible bean which is annotated using @Component annotation. This agency you lot don't to declare that edible bean using the <bean> tag in addition to inject the dependency, it volition live on done automatically past times Spring. This functionality was enabled in addition to disabled using <context:component-scan> tag.

Now that you lot know what does @Component annotation does let's come across what does @Service, @Controller, in addition to @Repository annotation do. They are zip but the specialized cast of @Component annotation for sure as shooting situations. Instead of using @Component on a controller cast inward Spring MVC, nosotros usage @Controller, which is to a greater extent than readable in addition to appropriate.

By using that annotation nosotros create 2 things, outset nosotros declare that this cast is a Spring edible bean in addition to should live on created in addition to maintained past times Spring ApplicationContext, but also nosotros signal that its a controller inward MVC setup. This latter belongings is used past times web-specific tools in addition to functionalities.


For example, DispatcherServlet volition human face for @RequestMapping on classes which are annotated using @Controller but non alongside @Component.

This agency @Component in addition to @Controller are same alongside abide by to edible bean creation in addition to dependency injection but after is a specialized cast of former. Even if you lot supersede @Controller annotation alongside @Compoenent, Spring tin automatically notice in addition to register the controller cast but it may non piece of work equally you lot await alongside abide by to asking mapping. You tin farther see, Spring Master Class course on Udemy for to a greater extent than details close these annotations.

Same is truthful for @Service in addition to @Repository annotation, they are a specialization of @Component inward service in addition to persistence layer. H5N1 Spring edible bean inward service layer should live on annotated using @Service instead of @Component annotation in addition to a trammel edible bean inward persistence layer should live on annotated alongside @Repository annotation.

By using a specialized annotation nosotros hitting 2 birds alongside ane stone. First, they are treated equally Spring edible bean in addition to minute you lot tin position exceptional conduct required past times that layer.

For example, @Repository's non exclusively helping inward annotation based configure but also grab Platform specific exceptions in addition to re-throw them equally ane of Spring’s unified unchecked exception.

Though for that you lot also demand to declare org.springframework.dao.annotation.PersistenceExceptionTranslationPostProcessor equally Spring edible bean inward your application context.

This edible bean postal service processor adds an advisor to whatever edible bean that’s annotated alongside @Repository thence that whatever platform-specific exceptions are caught in addition to and thence rethrown equally ane of Spring’s unchecked information access exceptions. You tin also come across Spring Framework 5: Beginner to Guru on Udemy for to a greater extent than details.

This is also ane of the oftentimes asked Spring Interview Question in addition to a pop concept from the Spring certification perspective. You volition give away a distich of questions based on these annotations in addition to their usage inward Spring professional person certification examination too.

How does Component Scanning piece of work inward Spring?

From Spring 2.0, Spring provides <context:component-scan> and annotation-driven dependency injection to automatically notice in addition to register Spring edible bean instead of specifying them inward the XML file. But, it exclusively scans @Component in addition to does non human face for @Controller, @Service in addition to @Repository inward general. They are scanned because they themselves are annotated alongside @Component.

Just accept a human face at @Controller, @Service, in addition to @Repository annotation definitions:

@Component
populace @interface Service {
….
}


@Component
populace @interface Repository {
….
}


@Component
populace @interface Controller {
…
}

Thus, it’s non incorrect to tell that @Controller, @Service, in addition to @Repository are exceptional types of @Component annotation. <context:component-scan> picks them upwards in addition to registers their next classes equally beans, merely equally if they were annotated alongside @Component.

They are scanned because they themselves are annotated alongside @Component annotation. If you lot define your ain custom annotation in addition to annotate it alongside @Component, in addition to thence it volition also acquire scanned with <context:component-scan>.

If you lot desire to larn to a greater extent than close dependency injection, auto-wiring in addition to dissimilar types of configuration inward Spring e.g. XML based, annotation-based in addition to Java configuration inward Spring, I propose you lot accept the Difference between @RestController in addition to @Controller inward Spring MVC?
How Spring MVC plant internally?
What is the usage of DispatcherServlet inward Spring MVC?
How to enable Spring safety inward a Java spider web application?
Difference between @RequestParam and @PathVariable inward Spring MVC?
Spring inward Action past times Craig Walls
REST alongside Spring Master Class past times Eugen Paraschiv

Thanks for reading this article thence far. If you lot similar this article in addition to thence delight part alongside your friends in addition to colleagues. If you lot conduct hold whatever inquiry or feedback in addition to thence delight drib a note.